Big spots on butterfly wings actually can mimic the eyes of predators, a new study finds, reviving a partly discredited textbook truth with fresh evidence.

In lab tests, images of butterflies with big spots on their wings spooked hungry little songbirds about as much as images of real, predatory owls did, says Johanna Mappes of the University of Jyväskylä in Finland. Yet butterfly images were only about half as likely to startle the birds when researchers removed the eyespots or reversed their colors, Mappes and colleagues report April 8 in Proceedings of the Royal Society B.

The experiment shows that conspicuous contrast by itself doesn’t give these wing spots their shock value, Mappes says. If the effect is instead due to a resemblance to predators’ eyes — an old and now disputed idea — that advantage could have nudged along the evolution of more realistic eyespots on wings.

This article is only available to Science News subscribers. Already a subscriber? Log in now. Or subscribe today for full access.